Palladium and palladium alloys are extensively used in a variety of industrial applications including the fabrications of jewelry, optical devices and electronic circuits and devices. Palladium and its alloys are attractive because of chemical inertness, surface luster and high electrical conductivity as well as excellent surface property, particularly for electrical contacts. In many applications, chemical inertness is highly advantageous for long life and high reliability. This is particularly true for applications in electrical and electronic devices.
Because of chemical inertness and reasonable surface hardness, palladium is especially attractive as an electrical contact material in electrical connectors, switches, etc. Various palladium alloys such as palladium silver and palladium nickel are also useful for the same applications. Indeed, because of the increasing cost of gold, palladium becomes more attractive economically as a contact material and as a surface material. In many applications where gold is used, it is often economically attractive to use palladium provided an inexpensive and efficient method of plating ductile and wear resistant palladium is available.
Commercially attractive processes for applying palladium films require high plating rates. Such plating rates often lead to undesirable film properties. In many such processes the palladium film is found to be brittle and susceptible to cracking. When used in electrical contact applications, there is a high incidence of failure due generally to palladium film problems. Often palladium film properties can be improved by drastically reducing plating rates, but such a solution is economically unsatisfactory. It is highly desirable to develop a simple, reliable, rapid process for rendering brittle palladium films ductile so as to be of use in various applications, including electrical connectors.
Palladium plating processes have been described in a number of references, including U.S. Pat. No. 1,970,950, issued to E. M. Wise on Aug. 21, 1934; U.S. Pat. No. 1,993,623, issued to A. R. Raper on Mar. 2, 1935; U.S. Pat. No. 3,920,526, issued to J. J. Caricchio, Jr. et al on Nov. 18, 1975; U.S. Pat. No. 1,921,931, issued to A. R. Powell et al on Aug. 8, 1933; U.S. Pat. No. 3,544,435 issued to H. C. Angus on Dec. 1, 1970; U.S. Pat. No. 3,458,409, issued to S. Hayashi et al on July 29, 1969; U.S. Pat. No. 2,452,308, issue to G. C. Lambros on Oct. 26, 1948 and U.S. Pat. No. 3,150,065, issued to G. D. Fatzer on Sept. 22, 1964.